Weed Warriors: The Upper Hand After the Drought

This past season, many farmers got an unwanted education in what can go wrong with weed control when a massive drought occurs. In the words of University of Missouri Extension weed scientist Kevin Bradley: "Just about everything."

Yet failure is often a good teacher—if you allow it to be. The lessons you learned in 2012 should be top of mind as you prepare for 2013 and what could well be another dry year, if current weather projections become a reality.

For starters, you probably will need to step up your weed management practices.

"Weed control is going to be more challenging, not simpler, in the years ahead," contends Aaron Hager, University of Illinois Extension weed scientist.

Hager and other weed scientists encourage you to leverage what you probably already know to eliminate weeds and capture more yield.

Their key points include:

Develop a systematic approach to weed control.

Don’t just control weeds; start clean to prevent them from getting established.

Use a number of different active ingredients, including some with residual.

Rotate crops if it makes sense, but be mindful of potential herbicide carryover from this past season.

Apply full labeled rates.

While you’re at it, read product labels to make sure you get the weeds you need to control in the time frame required.

Stay on top of any resistant weed problems; chop them by hand if need be, so they can’t go to seed.

While these practices don’t guarantee success, they will help you get a strong start this spring, and that will put you in position for a winning season in the battle against weeds.

How to implement a multistep weed control strategy this growing season

Corn and soybeans don’t care for prolonged hot weather, but some weeds sure do. Palmer amaranth, waterhemp and other heat-loving weeds thrived this past summer as temperatures soared across much of the country.

Many farmers’ best efforts failed to keep weeds at bay, notes Kevin Bradley, University of Missouri Extension weed scientist.

"I couldn’t begin to add up all the things that went wrong with our weedcontrol efforts last year," Bradley says.

Unusually warm spring temperatures in 2012 encouraged weeds in the state to emerge a good month to five weeks ahead of schedule. Because of their advanced growth, many weed populations were able to withstand farmers’ burndown herbicides. Preemergence products with residual control didn’t fare much better.

"They didn’t work well here last year because we didn’t have enough rain to activate them," Bradley says.

The actively growing weeds simply hardened off or grew to a size that prevented anything farmers poured from a jug to stop them. Scenarios similar to those in Missouri played out in other drought-hit states as well.

Unfortunately, that means weeds are poised to produce banner populations in farmers’ fields again this spring, says Aaron Hager, University of Illinois Extension weed scientist.

He is particularly concerned about multiple-herbicide-resistant waterhemp and glyphosate-resistant waterhemp. The latter is present in at least 75% of the 102 counties in Illinois.

"We color in more counties on our state map for waterhemp every year," Hager reports.

A strategic control approach and a change of mindset are needed if farmers are to get serious about putting a chokehold on weed problems in 2013, notes Ford Baldwin, owner of Practical Weed Consultants LLC and retired University of Arkansas Extension weed scientist. In his opinion, that means being proactive about prevention and not just control. "You need tillage diversity, herbicide trait diversity and crop diversity," he advises.

Hager tells Illinois corn and soybean growers to start the season with a soil-applied herbicide to tackle tough weeds such as giant ragweed, horseweed, morningglory and waterhemp.

Jesse Flye starts each season with a burndown product on every acre of corn and soybeans he grows. Beyond that, he strives to include four to five different active ingredients each year in his corn and soybean weed-control programs. (See "Whip Those Weeds".)

"We won’t ever go back to using just one herbicide for weed control, even if it’s a silver bullet," says Flye, who farms 12,000 acres of corn, cotton, rice, soybeans and wheat with his dad, Marty White, and brother, Logan White, near Trumann, Ark.

The men added 1,500 acres of corn into their crop rotation program two years ago. Corn allows them to use a different set of herbicide modes of action in their fields to take out stubborn populations of Palmer amaranth.

The practice worked so well that Flye plans to boost his corn crop to 3,000 acres this year.

"Corn is more important to us from a weed management perspective than the good grain prices, even," Flye says.

Carryover cautions. Crop rotation is usually a valuable ally in the war on weeds. But farmers need to take a cautious approach with it this season as some fields still contain left-behind herbicides that didn’t activate because of a lack of moisture, Bradley says.

"If you haven’t given much thought to whether herbicide carryover will be a problem this spring, don’t wait to figure that out," he encourages.

Bradley notes that Missouri farmers are spraying more fomesafen in soybeans to knock out severe waterhemp populations, though it can cause injury in corn if farmers rotate to it in fields where the herbicide is still present.

He offers an easy and inexpensive idea farmers can use to tell if carryover herbicides will be a problem in a specific field. A month prior to planting corn, he recommends, pull half a dozen soil samples from across a field and place a handful of dirt from each sample in a cup or jar. Plant some corn seed in each cup and watch it sprout. In about a week, you will see whether any herbicide residue is left from the previous year in that soil.

"If the corn shows signs of injury, you’ll know it before you plant and you can keep from making a 500-acre or worse mistake," Bradley says.

He adds that while agronomic laboratory tests can provide an accurate analysis and report on the presence of a herbicide in the field, such information is often difficult to decipher.

"It’s hard to know whether 15 parts per billion of something in the soil will hurt your corn. A simpler thing is to just do a soil bioassay, and it’s the cheapest thing to do," he says.

Overlapping herbicides is another tool that’s gaining traction with farmers in the Midwest. It is a mainstream practice in the mid-South and South, where it was first used in cotton.

Regardless of what products and practices farmers use to control weeds, scientists say they must use full labeled herbicide rates for optimum results.

"Skimping on rates can set up a scenario for resistance," Bradley says.

Adds Hager: "Everything is going to be more complex with weed control in the future, not simpler. Farmers who accept that as fact will be in a good position to take control of their weed problems this season."

Whip Those Weeds

Jesse Flye wishes he knew six years ago what he knows now: an effective weed control program requires a strategic approach each season with more than one kind of ammunition. "I wish someone had told me back then how bad these weeds can be, but maybe I wouldn’t have listened," he says, only half joking.

But Flye is listening now and taking action to knock out weeds.

Flye’s weed-control program in corn involves the use of four to five different active ingredients. He starts out with a burndown application of Gramoxone (paraquat) in the spring. He then applies Dual (metolachlor) behind the planter to take out annual grasses and small-seeded broadleaf weeds. Once the corn is emerged, he applies a tank mix of atrazine, Roundup and Laudis (tembotrione) for residual control of grass and broadleaf weeds, including herbicide-resistant Palmer amaranth.

For soybeans, Flye rotates between the Roundup Ready and LibertyLink systems. He prefers the former system because of its lower cost and the yield advantage he sees on his farm. However, he uses the latter system on about 20% of his acreage to control severe Palmer amaranth pressure.

"Some of our rental ground we’ve started farming has a pretty foul seed bank, and I’d be afraid of going with Roundup only," he says.

Trading spaces. Ford Baldwin encourages farmers to rotate between Roundup Ready and LibertyLink technologies in soybeans and to work in conventional crops whenever possible.

"If you follow corn with Roundup Ready soybeans one year, use LibertyLink soybeans the next year after corn," advises Baldwin, owner of Practical Weed Consultants LLC and former University of Arkansas Extension weed scientist.

For both soybean systems, Flye’s herbicide program includes a burndown application of Gramoxone mixed with 32% fertilizer and water.

"We have found the fertilizer makes an excellent drift retardant; that is the main reason we include it in our burndown program," Flye says. He adds that he uses the same technique in corn as well.

"With the corn, you get the added benefit of getting some of your nitrogen out [on the field]," he explains.

In soybeans, either right before planting or immediately after, he makes an application of Valor (flumioxazin). "We like to overlap our pre-emerge herbicides; we believe that gives us the best control results," he says.

Overlapping products is useful when farmers match the biology of the weed, when it grows, to the herbicide application timing, says Kevin Bradley, University of Missouri Extension weed scientist.

Diversity pays off. Once Flye’s soybean crop reaches the second trifoliate, he applies either Roundup (glyphosate) or Liberty (glufosinate), depending on which system he’s using in a particular field, in addition to Prefix, a combination of S-metolachlor and fomesafen. Bradley says the LibertyLink system works well as long as growers understand they need to use full rates, spray weeds under 3" tall and get good coverage.

Flye says his weed control costs across crops have more than doubled, from an average of $30 an acre to $70 an acre in the past six years, yet he believes the results are worth the expense.

"With grain prices what they are today, it’s a good time to use these herbicides, especially the pre-emerge products," he says. "We feel like they’re a good investment."